This proposal requests funds for continuing investigation of ovarian follicular selection. This term refers to the processes which regulate selective growth of only a few follicles in the vertebrate ovary to final maturation and ovulation. The reptilian ovary is studied because reptiles exhibit several patterns of ovulation, and the ovarian follicles are large and arranged in a simple size-gradation. A general hypothesis for the control of follicular selection is proposed: that differential follicular vascularity, augmented by local effects of steroid hormones and histamine, results in biased maturation of some follicles, growth and then atresia of others, and no growth of still others. Various components of this hypothesis will be tested. Blood flow rate to follicles of different size will be measured with radioactive microspheres and binding of 131I FSH to follicles in vivo and in vitro. The influence of estradiol and progesterone on thecal vessel permeability will be studied. Patterns of steroid secretion from follicles of different size will be determined using radioimmunoassay. The influence of gonadotropins, steroid hormones and compound 48/80 on histamine levels in the follicular wall and thecal mast cells will be determined. Possible effects of histamine on thecal vessel permeability will be considered. Synchrony of growth initiation of primordial follicles in different reptilian species, and the influence of gonadotropin levels on this synchrony, will be determined. BIBLIOGRAPHIC REFERENCES: Jones, R. E., Fitzgerald, K. T., and Tokarz, R. R. 1977. Endocrine control of clutch size in reptiles. VII. Compensatory ovarian hypertrophy, following unilateral ovariectomy in Sceloporus occidentalis. Gen. Comp. Endocrinol. (in press). LaGreek, F. T., and Jones, R. E. 1977. Endocrine control of clutch size in reptiles. VIII. Antiestrogenic effects of clomiphene citrate in the lizard Anolis carolinensis. Biol. Reprod. (in press).